Electrical heating element and fitting assembly

ABSTRACT

A heating element includes an elongated tubular sheath which confines a resistance wire supported by a thermally conductive electrical insulation material which extends to a position flush with the end surface of the sheath. Each end portion of the heating element is supported by a bulkhead fitting which is formed of sheet metal and includes a tubular wall portion having helical convolutions defining external threads. A radial flange portion projects outwardly from the tubular wall portion, and another portion of the fitting firmly engages the outer surface of the sheath. The flush end surfaces of the insulation material and the sheath are spaced inwardly from the end surface of the fitting to define a cavity, and a thermosetting sealant material is disposed within this cavity and the space defined between the outer surface of the sheath and the helical convolutions.

Unlted States Patent 1 1 3,930,140 Pease 1 *Dec. 30, 1975 [5 ELECTRICALHEATING ELEMENT AND 2,625,634 1 1953 Temple 174/77 R I T NG ASSEMBLY3,354,294 11/1967 Kollar et al. 219/536 [76] Inventor: James F. Pease,5805 F lk t FOREIGN PATENTS OR APPLICATIONS Drive, Dayton, Ohio 45459461,239 2/1937 United Kingdom 174/77 R 1 Notice: The portion of the termof this 663,233 12/1951 United Kingdom 174/77 R atent b tt A 18,1989, gb 6 52 2;: e pr Primary ExaminerC. L. Albritton Attorney, Agent, orFirm-Jacox & Meckstroth [22] Filed: Mar. 25, 1974 I 21 Appl. No.:454,291 ABSTRACT Related U.S. Application Data Continuation-impart ofSer.' No. 334,002, Feb. 20, 1973, Pat. No. 3,800,415, which is adivision of Ser. No. 244,516, April 17, 1972, Pat. No. 3,732,398, and acontinuation-in-part of Ser. No. 194,742, Nov. 1, 1971, abandoned.

U.S. Cl. 219/316; 174/77 R; 219/318;

A heating element includes an elongated tubular sheath which confines aresistance wire supported by a thermally conductive electricalinsulation material which extends to a position flush with the endsurface of the sheath. Each end portion of the heating element issupported by a bulkhead fitting which is formed of sheet metal andincludes a tubular wall portion having helical convolutions definingexternal threads. A radial flange portion projects outwardly from thetubular wall portion, and another portion of the fitting firmly engagesthe outersurface of the sheath. The flush end surfaces of the insulationmaterial and the sheath are spaced inwardly'from the end surface of thefitting to define a cavity, and a thermosetting sealant material isdisposed within this cavity and the space defined between the outersurface of the sheath and the helical convolutions.

10 Claims, 4 Drawing Figures ELECTRICAL HEATING ELEMENT AND FITTINGASSEMBLY RELATED APPLICATION Thisapplication is-a continuation-in-partof application Ser. No. 334,002, filed-.Feb. 20, 1973, now issued asU.S. ,Pat. No. 3,800,415 which is a division. of Ser.. No. 244,516,filed Apr. -17, .1972, U.S.- Pat. No. 3,732,398, a continuation-in-partof Sen-No. 194,742, filed Nov.-l, 1971, abandoned.

BACKGROUND OF THE I VENTION" The present invention is directed to thetype of elecitricalheating element and fitting assembly disclosed in Theends of the wire are attached to corresponding,

terminal pins which project axially from the end portions of the sheath.,A. machined metal fitting is commonly brazed or soldered to the end.portions of the sheath.

,To protect the dry rigid magnesium oxide insulation materialandhermetically seal it against moisture, the material is sandblasted ormechanically removed from each end or tip portion of the sheath to,define an annular cavity surrounding the projecting terminal pin. Thiscavity is then filled with a sealant material such as an epoxy resin,for example, as illustrated in U.S. Pat. No. 3,354,294., These.sandblasting and filling operations require substantial time and addsignificantly to the cost of producing the heating element.

The above patent applicationdiscloses a novel and an improved means forsecuring the end portions of a sheath-type heating element to the wallof a liquid heating tank or vessel. This means includes a tubularbulkhead bushing or fitting which is drawn from sheet metal such asbrass and is deformed to define helical convolutions which form externalthreads for receiving a mating drawn sheet metal nut. The bulkheadfittingis secured and sealed tothe corresponding end portion of thesheath by soft solder which forms an electrical ground connectionbetween the end portion of the sheath and. the fitting so that .thesheath can be grounded through the fitting by a suitable ground wireattached to the fitting through a ring-type-terminal.

SUMMARY oF THE INVENTION The present invention is directed to animproved electricalheating element and bulkhead fitting assembly whichsignificantly reduces the cost of manufacturing the assembly byeliminating operations for preparing the heating element to receive thefittings and by simplifying the assembly of the fittings onto theheating element and hermetically sealing the heating element all in oneassembly operation. That is, the present invention eliminates the needfor sandblasting the thermally conductive insultation material from eachend portion of the sheath of the heating element and provides forhermetically sealing the insulationmaterial assembling the fitting ontothe heating element. The invention also provides a simplified means forforming a positive electrical ground between the bulkhead fitting andthe'end portion of the sheath without soldering the fitting to thesheath. Thus, the invention eliminates the need. for washing the fittingafter the soldering operation to remove the soldering flux, and furtherprovides for minimizing the gauge of the sheet metal which is used forproducing the fitting.

The above features and advantages and other advantages of theinventionxwill be clearly apparent from the.

following description, the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan'view of a heatingelement and fitting assembly constructed in accordance with theinvention and shown mounted on the wall of a liquid heating vessel; Y

FIG. 2 is an enlarged fragmentary axial section of a heating element andfitting assembly;

FIG. 3 is an enlarged axial section similar to FIG 2 and illustratingthe method of assembling a .fittingonto an end portion of the heatingelement; and

FIG. 4 is an enlarged fragmentary section showing another embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I The immersion heating element10 shown in FIG. 1 is illustrative of the type commonly mounted withinthe sump of an automatic dishwashing machine for heating waterand foralso heating air during the drying period of the washing cycle. Theheating element 10 includes a metallic sheath 12 which is usually formedfrom stainless .steel or nickel alloy tubing and has a'circularcrosssectional configuration While the sheath 12 shown in FIG.. 1 isgenerally circular, the sheath may be formed in practically anyconfiguration such as, for example, rectangular with rounded corners orserpentine shaped.

The sheath l2 enclosed a high resistance conductor or wire 13 havingends connected to corresponding low resistance terminal pins 14 whichextend concentrically through the end portions 15 of the heating elementto.

terminal connectors 16. A thermally conductive electrical insulation 18such as magnesium oxide, surrounds the wire 13 and each terminal pin 14and supports the wire andpins concentrically within the sheath 12.

15 of the heating element 10 extends througha corresponding circularhole or'opening 19 (FIG. 2) formed within a bulkhead or wall 20 such asthe wall which within the heating element during the operation ofdefines the sump of an automatic dishwashing machine. Each end portion15 of the heating element 10 is secured to the wall 20 by a fittingassembly which includes a tubular bulkhead fitting 25 (FIG. 2) formed bydrawing and deforming a sheet metal disk in successive or progressivesteps. Since thefittings 25 mounted on both end portions 15 -of theheatingelement 10 are identical, only one will be described in detail.

In accordance with the present invention, each fitting 25 includes aflange ,portion 28 which is. partially formed by an outwardly projectingradial flange wall 29. The wall 29 has an outer periphery integrallyconnectedto an inwardly projecting radial flange wall 31 which extendsto form a frusto-conical hubportion 32 defining a circular openinghaving a diameter slightly As shown in the above application, each endportion.

3 less than the outer diameter of the sheath 12. r r

The fitting 25 further includes a cylindrical wall portion 34 whichextends from the flange wall 29 and which is adapted to receive a rubbergrommet 36 (FIG. 1) mounted within the corresponding opening 19 withinthe wall 20 when the heating element is installed within the wall. Thecylindrical wall portion 34 connects with a tubular wall portion 38having helical convolutions 39 which define corresponding externalhelical threads. As a result of the uniform wall thickness of thefitting 25, the convolutions 39 provide the tubular portion 38 with acorrugated wall configuration in axial cross-section as illustrated inFIG. 2. Preferably the inner diameter of the convolutions 39 issubstantially the same as the outer diameter of the sheath 12 as shownin FIG. 2. The convoluted tubular portion 38 connects with a cylindricalportion 41 which preferably projects inwardly and has an inner diameterslightly less than the outer diameter of the sheath 12 so that thecylindrical portion 41 firmly engages the sheath 12 in press-fitrelation.

'As shown in H0. 2, the end surface 42 of the insulation material 18 isflush with the end surface 43 of the sheath l2, and these flush endsurfacesare located inwardly from the outer end surface 44 of thefitting 25. A water-tight seal is formed between the end portion of thesheath l2 and the bulkhead fitting 25 by a sealant material 45.Preferably, the sealant material 45 consists of a heat activatedthermosetting epoxy resin. This material fills not only the annularspace or cavity around the terminal pin 14 between the end surface ofthe fitting 25 and the flush end surfaces of the sheath l2 andinsulation material 18, but'also fills the space defined between'eachconvolution 39 and the outer surface of the sheath 12. The sealantmaterial 45 also fills the space-between the parallel walls 29 and 31 ofthe flange portion 28 as well as the space defined between thecylindrical wall portion 34 and the outer surface of the sheath 12.

Referring to FIG. 3, each of the bulkhead bushings or fittings 25 isassembled onto the corresponding end portion 15 of the heating elementin the following manner; The hub portion 32 of the fitting 25 is pressedonto the end portion of the sheath 12 until the sheath projects'afraction of an inch into the fitting as indicated in FIG. 3.1Apredetermined quantity of heat activated liquid epoxy resin material 45is injected or poured into the fitting 25 so that the material 45 fillsthe space within the flange portion 28 of the fitting and the spaceabove the flush end surfaces of the sheath l2 and insulation material 18to a level as generally indicated in FIG. 3. The fitting 25 is thenpressed further onto the end portion of the heating element 12 until thefitting 25 is positioned as shown in FIG. 2.

During this pressing operation, the epoxy resin material 45 fills thespace between the convolutions 39 and the outer surface of the sheath l2andresults in filling the annular space or cavity surrounding theterminal pin 16 between the end surface of the fitting 25 and the flushend surfaces of the sheath 12 and insulation material 18. The heatingelement assembly is then heated within an oven to activate the epoxyresin material 45 and to set the material to a rigid condition forming apositive hermetic seal between the fitting 25 and the corresponding endportion 15 of the heating element 10. When the heating element isinstalled within the tank wall 20, the rubber grommets 36 formwater-tight seals between the flange portions 28 of the fittings 25 andthe tank wall in response to tightening of mating tubular sheet metalnuts 50 threaded onto the tubular portions 38 of the fittings asshown inthe above application. r

Referring to FIG. 4, a modified form of a heating element and fittingassembly includes a tubular bushing or fitting 50 having a cylindricalwall portion 54 which corresponds with thecylindrical wall portion 34 ofthe fitting 25 shown in FIG. 2 and is adapted to receive the rubbergrommet 36. An outwardly projecting radial flange portion 56 isconnected to the cylindrical wall portion 54 by a curved neck or hubportion 58 which projects inwardly from the cylindrical wall portion 54and firmly engages the outer surface of the metallic sheath 12. thus theneck or hub portion 58 serves the same function as the hub portion 32 ofthe embodiment shown in FIGS. 2 and 3, that is, to confine the sealantmaterial 45, to provide a tapered or curved lead surface for insertingthe sheath 12 into the fitting 50 and to cooperate with the portion 41to form an electrical ground between the sheath and the fitting. Inother respects, the fitting 50 is constructed substantially identical tothe fitting 25.

From the drawing and the above description, it is apparent that aheating element and fitting assembly constructed in accordance with thepresent invention, provides desirable features and advantages. Forexample, the bulkhead bushing or fitting 25 or 50 is quickly andeconomically produced from a disc of sheet metal and assembles onto anend portion 15 of a heating element 10 in a manner which eliminates theoperation of sandblasting an annular'cavity within the end portion ofthe metal sheath 12 around the terminal pin 14. The epoxy resin materialnot only forms a positive hermetic seal for the end surface of theinsulation material 18, but also forms a water-tight seal between thefitting 25 or 50and the outer surface of the sheath 12. In addition, therigid epoxy resin forms a rigid solid mass between the convolutions 39and the end portion 15 of the heating element 10 so that the threadsformed by the convolutions 39 do not collapse or deform when thecorresponding nut 50 is tightened with substantial torque.

The hub portion 32 of the fitting 25 or the hub portion 58 of thefitting 50 not only forms a tapered lead surface receiving the tipportion of the heating element 10 in a press-fit relation, but alsoforms a positive electrical ground connection between the outer surfaceof the sheath l2 and the fitting 25 or 50. As mentioned above, anothersuch ground is formed between the cylindrical portion 41 and the sheath.

While the forms of heating element and fitting assembly herein describedconstitute preferred embodiments of the invention, it is tobe.understood that the invention isnot limited to these precise forms ofassembly, and that changes may be made therein without departing fromthe scope and spirit of the invention.

The invention having thus been described, the

following is claimed:

l. A heating element and fitting assembly for mounting within spacedopenings in a wall of a liquid heating' vessel, said assembly comprisingan elongated tubular LII sheath having opposite end portions, anelectrical resistance heating element extending longitudinally withinsaid sheath and supported therein by a thermally con- 'ductive insulatormaterial, an electrical connector connected to each end of said heatingelement and projectsheath, a sheet metal tubular fitting mounted on eachsaid end portion of said sheath and adapted to extend through thecorresponding opening within the wall, each said fitting having asubstantially uniform wall thickness and including an outwardlyprojecting peripheral flange portion integrally connected to a tubularwall portion, said flange portion of each said fitting includes aradially outwardly projecting annular wall integrally connected to aradially inwardly projecting annular wall providing said flange portionwith a double wall thickness, said tubular wall portion of each saidfitting having a deformed wall configuration forming an outwardlyprojecting threaded portion around said sheath, each said fittingincluding a portion in radial gripping engagement with the correspondingsaid end portion of said sheath to form an electrical conductortherewith and for securing said fitting to said end portion of saidsheath, and means forming a liquid-tight seal between each said fittingand said sheath.

2. A heating element and fitting assembly as defined in claim 1 whereineach said fitting includes an annular portion projecting generallyaxially from said radially inwardly projecting annular wall and havingsaid gripping engagement with said sheath.

3. A heating element and fitting assembly for mounting within spacedopenings in a wall of a liquid heating vessel, said assembly comprisingan elongated tubular sheath having opposite generally cylindrical endportions, an electrical resistance heating element extendinglongitudinally within said sheath and supported therein by a thermallyconductive insulator material, an electrical connector connected to eachend of said heating element and projecting through the correspondingsaid end portion of said sheath, a sheet metal tubular fitting mountedon each said end portion of said sheath and adapted to extend throughthe corresponding opening within the wall, each said fitting having asubstantially uniform wall thickness and including an outwardlyprojecting peripheral flange portion integrally connected to a tubularwall portion, said tubular wall portion of each said fitting having adeformed convoluted wall configuration forming an outwardly projectingthreaded portion around said sheath, each said fitting including aninwardly projecting substantially annular neck portion having an innerdiameter substantially the same as the outer diameter of thecorresponding said end portion of said sheath, and means forming aliquid-tight seal between each said fitting and said sheath.

4. A heating element and fitting assembly as defined in claim 3 whereinsaid tubular wall portion of each said fitting includes said annularneck portion.

5. A heating element and fitting assembly as defined in claim 3 whereinsaid annular neck portion of each said fitting connects said flangeportion to sai threaded portion.

6. A heating element and fitting assembly as defined in claim 3 whereinsaid annular neck portion of each said fitting is in radial grippingengagement with said sheath.

7. A heating element and fitting assembly as defined in claim 3 whereinsaid tubular wall portion of each said fitting includes a smoothcylindrical wall portion extending from said threaded portion, and saidannular neck portion connects said cylindrical wall portion to saidflange portion.

8. A heating element and fitting assembly as defined in claim 7 whereinsaid cylindrical wall portion of each said fitting has an inner diametergreater than the outer diameter of said sheath to form an annular spacetherebetween, and said means forming said liquid-tight seal comprises asealing material within said annular space.

9. A heating element and fitting assembly as defined in claim 3 whereinsaid sheath has an end surface terminating within said tubular wallportion of each said fitting, and said insulator material extends toeach said end surface of said sheath and is generally flush therewith.

10. In a heating element and fitting assembly for mounting within spacedopenings in a wall of a liquid heating vessel and including an elongatedtubular sheath having opposite generally cylindrical end portions, anelectrical resistance heating element extending longitudinally withinsaid sheath and supported therein by a thermally conductive insulatormaterial, an electrical connector connected to each end of said heatingelement and projecting through the corresponding said end portion ofsaid sheath, a tubular fitting mounted on each said end portion of saidsheath and adapted to extend through the corresponding opening withinthewall, and means forming a liquidtight seal between each said fittingand said sheath, the improvement wherein each of said fittings has asubstantially uniform wall thickness and comprises a drawn sheet metaltubular wall portion, an integral peripherally extending sheet metalflange portion projecting outwardly from said tubular wall portion, saidsheet metal tubular wall portion of each said fitting having acorrugated wall configuration in axial crosssection to form an outwardlyand inwardly projecting convoluted threaded portion, and said convolutedthreaded portion of each said fitting extends around the correspondingsaid end portion of said sheath.

1. A heating element and fitting assembly for mounting within spacedopenings in a wall of a liquid heating vessel, said assembly comprisingan elongated tubular sheath having opposite end portions, an electricalresistance heating element extending longitudinally within said sheathand supported therein by a thermally conductive insulator material, anelectrical connector connected to each end of said heating element andprojecting through the corresponding said end portion of said sheath, asheet metal tubular fitting mounted on each said end portion of saidsheath and adapted to extend through the corresponding opening withinthe wall, each said fitting having a substantially uniform wallthickness and including an outwardly projecting peripheral flangeportion integrally connected to a tubular wall portion, said flangeportion of each said fitting includes a radially outwardly projectingannular wall integrally connected to a radially inwardly projectingannular wall providing said flange portion with a double wall thickness,said tubular wall portion of each said fitting having a deformed wallconfiguration forming an outwardly projecting threaded portion aroundsaid sheath, each said fitting including a poRtion in radial grippingengagement with the corresponding said end portion of said sheath toform an electrical conductor therewith and for securing said fitting tosaid end portion of said sheath, and means forming a liquid-tight sealbetween each said fitting and said sheath.
 2. A heating element andfitting assembly as defined in claim 1 wherein each said fittingincludes an annular portion projecting generally axially from saidradially inwardly projecting annular wall and having said grippingengagement with said sheath.
 3. A heating element and fitting assemblyfor mounting within spaced openings in a wall of a liquid heatingvessel, said assembly comprising an elongated tubular sheath havingopposite generally cylindrical end portions, an electrical resistanceheating element extending longitudinally within said sheath andsupported therein by a thermally conductive insulator material, anelectrical connector connected to each end of said heating element andprojecting through the corresponding said end portion of said sheath, asheet metal tubular fitting mounted on each said end portion of saidsheath and adapted to extend through the corresponding opening withinthe wall, each said fitting having a substantially uniform wallthickness and including an outwardly projecting peripheral flangeportion integrally connected to a tubular wall portion, said tubularwall portion of each said fitting having a deformed convoluted wallconfiguration forming an outwardly projecting threaded portion aroundsaid sheath, each said fitting including an inwardly projectingsubstantially annular neck portion having an inner diametersubstantially the same as the outer diameter of the corresponding saidend portion of said sheath, and means forming a liquid-tight sealbetween each said fitting and said sheath.
 4. A heating element andfitting assembly as defined in claim 3 wherein said tubular wall portionof each said fitting includes said annular neck portion.
 5. A heatingelement and fitting assembly as defined in claim 3 wherein said annularneck portion of each said fitting connects said flange portion to saidthreaded portion.
 6. A heating element and fitting assembly as definedin claim 3 wherein said annular neck portion of each said fitting is inradial gripping engagement with said sheath.
 7. A heating element andfitting assembly as defined in claim 3 wherein said tubular wall portionof each said fitting includes a smooth cylindrical wall portionextending from said threaded portion, and said annular neck portionconnects said cylindrical wall portion to said flange portion.
 8. Aheating element and fitting assembly as defined in claim 7 wherein saidcylindrical wall portion of each said fitting has an inner diametergreater than the outer diameter of said sheath to form an annular spacetherebetween, and said means forming said liquid-tight seal comprises asealing material within said annular space.
 9. A heating element andfitting assembly as defined in claim 3 wherein said sheath has an endsurface terminating within said tubular wall portion of each saidfitting, and said insulator material extends to each said end surface ofsaid sheath and is generally flush therewith.
 10. In a heating elementand fitting assembly for mounting within spaced openings in a wall of aliquid heating vessel and including an elongated tubular sheath havingopposite generally cylindrical end portions, an electrical resistanceheating element extending longitudinally within said sheath andsupported therein by a thermally conductive insulator material, anelectrical connector connected to each end of said heating element andprojecting through the corresponding said end portion of said sheath, atubular fitting mounted on each said end portion of said sheath andadapted to extend through the corresponding opening within the wall, andmeans forming a liquid-tight seal between each said fitting and saidsheath, the improvement wherein each of said fittings has asuBstantially uniform wall thickness and comprises a drawn sheet metaltubular wall portion, an integral peripherally extending sheet metalflange portion projecting outwardly from said tubular wall portion, saidsheet metal tubular wall portion of each said fitting having acorrugated wall configuration in axial cross-section to form anoutwardly and inwardly projecting convoluted threaded portion, and saidconvoluted threaded portion of each said fitting extends around thecorresponding said end portion of said sheath.